CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Common Stock	Additional Paid In Capital.	Retained Earnings Class A Common Stock	Retained Earnings Class B Common Stock	Retained Earnings	Accumulated Other Comprehensive Income	Class A Common Stock	Class B Common Stock	Total
Balance at beginning of period at Dec. 31, 2014								$ 4,315
Increase (Decrease) in Stockholders' Equity
Net income											$ 27,748
Net change in accumulated other comprehensive income								49			49
Balance at end of period at Sep. 30, 2015								4,364
Balance at beginning of period at Dec. 31, 2014								4,315
Balance at end of period at Dec. 31, 2015			$ 4,915	$ 136,910			$ 432,673	2,049			576,547
Balance (in shares) at Dec. 31, 2015	18,652	2,245
Increase (Decrease) in Stockholders' Equity
Net income							35,903				35,903
Net change in accumulated other comprehensive income								925			925
Dividends declared Common Stock:
Dividends declared Common Stock					$ (11,469)	$ (1,258)			$ (11,469)	$ (1,258)
Stock options exercised, net of shares redeemed				80							80
Stock options exercised, net of shares redeemed (in shares)	4
Repurchase of Class A Common Stock			(9)	(274)			(851)				(1,134)
Repurchase of Class A Common Stock (in shares)	(41)
Net change in notes receivable on Class A Common Stock				63							63
Deferred director compensation expense - Class A Common Stock				149							149
Deferred director compensation expense - Class A Common Stock (in shares)	4
Stock based compensation expense - performance stock units				381							381
Stock based compensation - restricted stock				189							189
Stock based compensation - restricted stock (in shares)	(2)
Stock based compensation expense - stock options				184							184
Balance at end of period at Sep. 30, 2016			$ 4,906	$ 137,682			$ 454,998	$ 2,974			$ 600,560
Balance (in shares) at Sep. 30, 2016	18,617	2,245